The invention concerns increasing the shelf life of an oil-in-water (o/w) microemulsion containing a biocidally active aza type compound for repeated use over an extended period as a dip or spray in the control of animal, particularly livestock, infestations or infections and the o/w microemulsion compositions needed to achieve this improvement as well as prolonged aza activity.
The treatment of animals by topical application of biocidal aza type o/w formulations, used as a dip, xe2x80x9cpour onxe2x80x9d or spray, are much in demand. Since the treatment of livestock, e.g. sheep, cattle, etc., requires repeated treatments over a long period to assure arrest of infestation or infection, it has been the practice to keep on hand sufficiently large quantities of the emulsion to cover the treatment period. As the solubility, and consequently the activity, of the aza compound is greatly improved in alkaline media, it has been the practice to add lime to the o/w emulsion. However, Ca(OH)2 precipitates in the presence of air to form calcium carbonate, an insoluble, rock-like solid which settles to the bottom of the holding tank. The adsorption of significant quantities of the aza compound in the calcium carbonate accompanies the precipitation so that the biocidal activity in soluble form in the emulsion is greatly reduced. For example, it was found that lime-treated Amitraz microemulsion showed a 60% reduction in activity after only 6-14 days storage at about 20xc2x0 C. At higher temperatures, 38xc2x0 C. which are often encountered in the field, the depletion of soluble aza compound in the emulsion is even greater and more rapid.
Accordingly, it is an object of this invention to overcome the above disadvantages by significantly extending the shelf life and the efficacy of o/w microemulsions containing a biologically active aza component.
Another object is to provide an improved o/w microemulsion for protecting livestock and domestic animals against pest infestation such as lice, ticks, mites etc. and infections causing harmful dermal disorders, such as fungus infections, e.g. mange.
Still other objects are to provide an improved o/w microemulsion containing a biocidally active aza compound and to a method for preparing the improved microemulsion.
In accordance with this invention there is provided a stabilized reservoir of o/w microemulsion containing a biocidally active aza type compound by addition of an alkaline buffering agent such as an inorganic Na, K and or NH4 salt of a phenol, a polyphenol or a weak acid, preferably a polybasic acid; an alkanol amine, such as a polyalkanol amino C2 to C4 alkane, e.g. triethanol amino methane; a polyamine salt of a weak acid or a mixture of these buffering agents. The buffering agent, which is incorporated in the microemulsion without the assistance of any Ca salt, is added in an amount sufficient to adjust the pH of the microemulsion to between about 6 and 14, preferably, for Amitraz, to a pH of between 8 and 10 and a pH of between 6-8 for Metsulfurons.
The active aza compounds referred to herein are active herbicidal or pesticidal compounds containing the aza group 
wherein the free valences on the carbon atom can form a double bond or are singly bonded to another atom or group. These aza bioactive agents include such compounds as Amitraz, Metsulfurons etc. containing the structure
R1xe2x80x94(X)xe2x80x94R2 
wherein one of R1 and R2 is a sulfur- and/or a nitrogen-containing heterocyclic radical having 3 to 5 carbon atoms in a 4 to 6 membered heterocyclic ring or alkenylphenyl, and the other of R1 and R2 is the same or is amidosulfuron, phenyl, sulfonylphenyl, phenyloxy, phenoxysulfonyl, or phenylamino where said phenyl radicals and heterocyclic radicals are optionally substituted with lower alkyl, halo, haloalkyl, cyano, C1 to C4 alkyl ether, a C1 to C4 ester, carboxy, ketone, and/or amino and X is 
where R3, R4, R5 and R6 are each individually selected from the group of hydrogen, lower alkyl, cyano and amino. Specific examples of effective aza compounds are disclosed in U.S. Pat. No. 5,731,264 and are also incorporated herein by reference.
The active compounds of this invention contain an aza radical as defined above. Specific and preferred examples of such biologically or herbicidally active compounds include Amitraz, Metsulfuron-methyl, Metsulftron, Thifensulfron, Chlorsulfron, Sulfometuron and the like.
Amitraz has the structure: 
This insecticidal, acaricidal compound has a half life of about 6 hours in water at a pH of 7, and is soluble in water to the extent of 1 mg/liter.
The heterocyclic sulfonyl urea, Metsulfuron-methyl, having the structure 
and Metsulfuron having the structure 
have similar half lives, as do other active aza compounds, such as sulfonyl urea (cyclosulfamuron) and those disclosed in U.S. Pat. No. 5,731,264. Of the above active compounds, Amitraz and Metasulfuron-methyl are most preferred.
The present buffering agents are added to an o/w microemulsion described and claimed in U.S. Pat. No. 6,255,350 the entire disclosure of which is incorporated herein by reference. The o/w microemulsion of this invention contains between about 0.01 and about 10 wt. % of the concentrate described in claim 1 of said issued patent which concentrate contains, by weight:
(a) between about 0.05 and about 25% of at least one active aza compound selected from the group consisting of Amitraz and an aza compound having the formula:
R1xe2x80x94(X)xe2x80x94R2 
xe2x80x83wherein one of R1 and R2 is alkenylphenyl, aminophenyl or a sulfur- and/or nitrogen-containing heterocyclic radical containing 3 to 5 carbon atoms in a 4 to 6 membered ring and the other of R1 and R2 is the same or is selected from the group consisting of amidosulfuron, phenyl, sulfonylphenyl, phenyloxy and phenyloxysulfonyl where said phenyl radicals and said heterocyclic radicals of R1 and R2 are optionally substituted with lower alkyl, halo, haloalkyl, cyano, C1 to C4 alkyl ether, C1 to C4 ester, carboxyl, ketone amido and amino and X is: 
xe2x80x83where R3, R4, R5 and R8 are each individually selected from the group consisting of hydrogen, lower alkyl, cyano, and amino,
(b) between about 2 and about 40% of a lipophilic lactam selected from the group consisting of C8 to C18 N-alkyl pyrrolidone, C8 to C18 alkyl caprolactam and a mixture thereof,
(c) between about 2 and about 20% of a moisture scavenging agent selected from the group consisting of a hindered carbopolyimide, a molecular sieve and a mixture thereof,
(d) between about 10 and about 80% of a lipophilic/hydrophilic mixture of having an overall HLB of 7 to 20, comprising at least two emulsifiers wherein at least two of said emulsifiers in the mixture are non-ionic and
(e) between 0 and about 15% of an aromatic oil.
After dilution of the concentrate with water, or water containing between about 0.001 and about 0.5 wt. % of salts such as the chlorides or sulfates of magnesium, calcium, iron etc. to form the microemulsion, between about 0.1 and about 1 wt. %, preferably 0.2-0.8 wt. %, based on total composition, of the present buffering agent is added. The microemulsions thus formulated with the present buffer replacing lime or other neutralizers, are stabilized with at least 95% aza activity retained over a period of at least a month up to 6 months or more.
The buffering agents employed herein, in addition to the specific examples recited above, include mixtures of sodium carbonate and sodium bicarbonate, sodium borate or perborate, sodium salts of other weak acids such as the polybasic acids represented by malonic, malic, glutaric, succinic and boric acids; sodium salts of phenols, e.g. cresol and polyphenols; amine salts of the foregoing acids; and the corresponding potassium or ammonium salts of the above sodium salts and mixtures of these buffering agents are also suitably employed in the o/w microemulsions of aza biocides. Of this group, the sodium carbonate/sodium bicarbonate 20/80-80/20 mixtures and corresponding potassium salt mixtures are most preferred. In general, the present o/w microemulsions contain between about 0.01 and about 5.0 wt. % of the buffering agent and between about 50 and about 500 ppm of the active aza component in the microemulsion. Preferably, 0.1-2 wt. % and most preferably 0.2-1 wt. % of the buffering agent is incorporated into the o/w emulsion to achieve a desirable pH. If desired, the pH can be further adjusted with NaOH or KOH which hydroxides are converted in the system to the corresponding carbonates.
Between about 1 and about 15 wt. % of an aromatic oil can also be added to the o/w microemulsion along with the buffer to further extend the microdroplets and the micellular structure. Suitable aromatic oils include alkyl naphthalenes, hydrogenated alkyl naphthalenes, vegetable oil and the like.
Having generally described the invention, reference is now had to the following examples which are presented to illustrate preferred embodiments but which are not to be construed as limiting to the scope of the invention as more broadly described above and defined in the appended claims.